(a) Technical Field
The invention generally relates to a wireless communication system and more particularly to a wireless communication system implementing adaptive frequency hopping.
(b) Description of the Related Art
A Bluetooth communication system is a frequency hopping communication system. Bluetooth includes an Adaptive Frequency Hopping (AFH) for selecting good channels to connect to other wireless device with AFH to prevent interference on a specific channel. A conventional “frequency hopping” technology is disclosed in U.S. Pat. Nos. 7,027,418 and 7,570,614. If two Bluetooth devices are connected to form a pico-net, one of the two Bluetooth devices is a master device and the other is a slave device. The AFH of Bluetooth includes an AFH channel map. One Bluetooth device may notify the other device which channel is good or bad according to the AFH channel map. The summation of good and bad channels is 79, as stipulated by the Bluetooth Specification. The AFH channel map is determined by the master device and the method of determination includes the following.
(1) The master device determines whether the channel is good or bad according to the status of reception and transmission on the channel.
(2) The master device transmits a signal to poll the channel status of the slave device. The slave device responds to the master device the channel status. Thus the master device can update the AFH channel map according to the channel status of both the master device and slave device.
Thus, it is clear that both of the master device and the slave device should be able to detect the performance of channels.
However, the conventional Bluetooth with AFH may only detect the channel quality of the channels currently in use but cannot acquire the channel quality of the rest of channels (which are not hopping in). Therefore, the problems have arisen:
(1) Once the channels in the AFH channel map are divided into a good and bad channel group, the AFH of Bluetooth implements frequency hopping and measures the channel quality within the good channel group. However, if there is an error made by the AFH channel map statistics or caused by temporary interference, in a good channel, the good channel is determined to a bad channel. After updating the AFH channel map repeatedly, the number of good channels becomes fewer. For example, there are 79 good channels in the AFH channel map. After that, AFH of Bluetooth repeatedly implements frequency hopping and measures the channel quality during a period of time, 30 channels may become bad channels. These 30 channels include actually bad channels, error in statistics, or temporary interference. Thus the number of good channels becomes 49. Then the master device updates the AFH channel map and notifies the slave device. As a result, the number of good channels may become fewer than the AFH standard threshold (at least 20 good channels) defined in the Bluetooth Specification after AFH repeatedly updates the AFH channel map.
(2) When the AFH of Bluetooth detects that the number of good channels are fewer than the standard threshold or wants to add good channels, the AFH of Bluetooth needs to set some of bad channels into good channels and update the AFH channel map. However, since the actual status of the new good channels originally considered as bad channels are unknown, Bluetooth transmission might be influenced. If the channel quality of the new channels is bad, the quality of frequency hopping by Bluetooth is seriously affected. In addition, the AFH of Bluetooth cannot remove the bad channels that are added by mistake until the AFH of Bluetooth updates the AFH channel map again.
Furthermore, more and more system manufacturers want to combine Wireless Local Area Network (WLAN) and Wireless Personal Area Network (WPAN) in a dual-mode. WLAN can cover farther transmission distance and provide a higher transmission speed to thereby communicate with external networks. For example, WLAN can use Asymmetric Digital Subscriber Line (ADSL) to connect an external internet. WPAN can provide the peer-to-peer data transmission in Digital Home system and cover closer transmission distance. The characteristic of WPAN is simple and electricity-saving.
Bluetooth has the highest marketing share and maximum number of users, and is the most widely used system In WPAN. WLAN and WPAN can be separately integrated into the transceiver of a Digital Home system. A Digital Home system may be a personal computer (PC), a notebook (NB), a smart phone, a set-top box, a television, a game console . . . etc. In this manner, the manufacturer may suffer from more complex design and higher cost, and take more time to develop products of WLAN and WPAN.
Despite the above mentioned limitations, Bluetooth has other advantages described below. First, Bluetooth and WLAN operate within a bandwidth of 2.4 GHz (ISM-band), which is free of charge. Bluetooth operates within 1 MHz bandwidth and includes 79 channels from 2402 MHz to 2480 MHz. On the other hand, WLAN operates within a bandwidth of 20 MHz in the G-mode and operates within a bandwidth close to 40 MHz in the 11 N-mode. The center frequency within the first channel of WLAN being the lowest frequency is 2412 MHz and the center frequency within the 11th channel of WLAN being the highest frequency is 2462 MHz. Further the center frequency within the 14th channel of WLAN is defined as 2484 MHz in some countries. Therefore, the channels used by Bluetooth and WLAN almost entirely overlap with each other. For example, if Bluetooth transmits data via a bandwidth which overlaps that of WLAN, the transmission quality of WLAN within the overlapped bandwidth can be seriously affected, and vice versa.